Question

I’m currently using IntelliJ IDEA for Java development, but I’m also interested in answers targeting other IDEs or general concepts for debugging Java code. Because this is a feature I’ve missed in a number of IDEs, I’m unsure if I’ve missed a workflow concept when transferring my debug habits from other languages.

Let’s say I’m writing some code in myapp.* while using framework classes from somelib.*. A typical stack trace may start in either package and may switch several times between them. Let’s also say I’m debugging under the assumption that there are bugs in my code and that there aren’t any in the library code. An example stack trace (showing only class names):

somelib.D (current stack frame)
somelib.C
myapp.Y
myapp.X
somelib.B
somelib.A

Normally, I’m not interested in the following types of exceptions and do not want the debugger to break on them:

• Thrown in somelib.B and caught in somelib.A. Either the library code is throwing exceptions to handle problematic state inside the library or to stop the application. In the latter case, I’m only interested in the exception message which hopefully tells me what’s wrong.

• Thrown in somelib.D and caught in somelib.C. The library code may use exceptions as a form of logic where a certain action is tried and an alternative route is taken in the case of a problem or where my code is notified by the problem by other means (e.g. returning a null reference where appropriate).

Types of exceptions I am interested in:

• Thrown in somelib.C or somelib.D and not caught in somelib.C or somelib.D. Here I want the debugger to break on the line in myapp.Y where I call the code from somelib.C.

• Thrown in myapp.X or myapp.Y, either caught or uncaught. Here I want the debugger to break on the line the exception is thrown.

IntelliJ IDEA gives me the options to select wether I want to break on caught or uncaught exceptions, or both and to restrict the location where the exception is thrown to a set of classes. These options don’t help much as I normally want to break on any exception, wether caught or uncaught, as long as code I’ve written is between the place it’s thrown and the place it’s caught, eventually.

Answer 1

It seems to be impossible to do exactly what I wanted in a convenient way. At the time of this question I was in the process of learning Java and teaching it to my fellow students, so a simple solution would have been favorable.

But with my current experience it seems reasonable to use the following approach:

1. Put catch (Trowable t) around each thread body, i.e. at the top level of Runnable.run() and static main(String[]) and log these “uncaught” exceptions to the console.
   • Care needs to be taken to not accidentally catch checked exceptions with these “catch-all” handlers, but to handle them as part of program logic.
2. When starting to debug, do not create any exception breakpoints.
3. As soon as an exception is logged to the console, create an exception breakpoint for it and try to make it get thrown again.
   • This should only happen unchecked exceptions (i.e. subclasses of RuntimeException) as other exceptions have to be explicitly caught and handled anyway.
   • As catching and handling unchecked exceptions normally isn’t part of a program’s logic, creating these exception breakpoints without constraints on the place it’s thrown should not catch any “false positives”.

An alternative is to skip the last two steps and instead create an exception breakpoint for RuntimeException. But this has a higher change of catching exceptions that are caught as part of the program logic.